Hello everyone, as iwas using this forum like 5years ago last time i built my first gaming rig. Now i need help again

Planning 3.5k euro on this one

2x 1080 ti asus rog poseidon i want to use with the rig
Need suggestions on CPU/Motherboard/SSD/watercooling for VGA and possible for cpu
Also im currently using 1200 antec psu will it fit the new gen 1080ti sli or should i buy new one instead

Yes, your Antec will handle the 1080 Ti cards with no problem
Pick your own case, or at least pick a few you like the look of and let us make suggestions from that. Case selection has a lot to do with your personal taste.
Honestly, I suggest lowering your budget and going with either a 6 core or 8 core CPU. You probably don't need or will ever use a 10 core to it's full potential, so this would probably be a more suitable build for you- https://uk.pcpartpicker.com/list/9MH9VY . but the money was in the budget so......

Yea up to 20, im something like hunter there and after latest graphic improvements my pc crashes like after 2-3h and its almost impossible to watch movie and playing a game (kinda used of that style of gaming)

My two $. Halve the budget, get everything mainstream platform has to offer, and spend 25% on a new GPU next year = more performance + 25% saved. Bonus points for not having to resort to SLI, just stay current with the best single GPU every year.

Or don't but then you don't need advice, just go out and buy silly things

But that is the problem with SLI on this card: you overspend today for performance that will perhaps be utilized for 60% of its potential and in one year, when its performance starts to show, you can get a single card that again probably maxes out your experience + newest tech, probably more silent/less power use, and better support. In addition, with a yearly or bi-yearly GPU upgrade you can also resell that card for good money. (And you get to scratch the upgrade itch which to me is a good thing )

On the other hand if you sell 2x 1080ti in 3 years, their value will have dropped a whole lot more and you take that hit on both cards too. Or are you saying 'I'll add a 2nd 1080ti in a year when they're cheaper?'

But ofc its not my money ^^

HEDT rig... is another route, and will yield more value for money (like @cucker tarlson suggests) but with 6c/12t now available on mainstream I don't really see the point unless you're really using the 40 lanes. You won't saturate PCI 3.0 8x8 with dual 1080tis. Also, if you get more than 6 cores on HEDT, you'll be losing in clockspeeds which won't benefit a gaming build, on the contrary even.

You'd lose what, 3-5 FPS worst case and only at 1080p. Not worth sacrificing clockspeed over - because lack of CPU grunt will result in stutter or lower MINIMUM fps, while scaling FPS losses translate to lower MAX fps. Note that when resolution goes up, 8x8 holds up much better, up to below 1 fps differences @ 4K, as the max FPS goes down.

But that is the problem with SLI on this card: you overspend today for performance that will perhaps be utilized for 60% of its potential and in one year, when its performance starts to show, you can get a single card that again probably maxes out your experience + newest tech, probably more silent/less power use, and better support. In addition, with a yearly or bi-yearly GPU upgrade you can also resell that card for good money. (And you get to scratch the upgrade itch which to me is a good thing )

On the other hand if you sell 2x 1080ti in 3 years, their value will have dropped a whole lot more and you take that hit on both cards too. Or are you saying 'I'll add a 2nd 1080ti in a year when they're cheaper?'

But ofc its not my money ^^

HEDT rig... is another route, and will yield more value for money (like @cucker tarlson suggests) but with 6c/12t now available on mainstream I don't really see the point unless you're really using the 40 lanes. You won't saturate PCI 3.0 8x8 with dual 1080tis. Also, if you get more than 6 cores on HEDT, you'll be losing in clockspeeds which won't benefit a gaming build, on the contrary even.

7820X should have similar performance. But it's not what HEDT used to be. Only 28 lanes and crappy pigeon poop TIM instead of solder. Honestly, if I was building a 1080Ti system, I'd go 6850K. 6c/12t, oc around 4300MHz but who uses 1080Ti SLI for anything less than 3440x1440 ? This CPU is gonna drive those cards pretty well if you're shooting for 100 fps. What you might need more than MHz is pci-e lanes running two such monstrous cards.

Seems to me that paring the fastest gaming CPU with a SLI setup is in a complete deadlock until we see pci-e 4.0 on a mainstream platform. That should provide enough bandwidth from 16 lanes to feed two high-end GPUs while being able to run the fastest available gaming CPU,which is traditionally a mainstream one (7700K,8700K).

Why iwant sli sys tem is more for multi instance games. Lets say i need couple instances of eve runing on 2 monitors while im playing league of legends or cs:goon third monitor. simple i dont want to load single card for it
Tbh not even planing 4k gaming atm. VR maybe.